The clinical utilization of a pointed hollow needle mounted inside a flexible catheter tube is well known in the medical art for the introduction of a catheter. In such a medical instrument, the catheter tube is positioned tightly around the needle in such a way as to allow the needle to slide and telescope along the length of the catheter tube. Before use, the tip of the needle is protruding slightly through the opening of the catheter tube to allow facile penetration through the skin. Upon puncturing of the skin and introduction of the needle, the distal end of the catheter tube is simultaneously brought into place inside the desired target body cavity of the patient, such as the inside of a blood vessel, for example a vein. The needle has then done its duty in assisting the introduction of the catheter and is withdrawn by being pulled backwards through the catheter. Upon release of the needle, the catheter is set in its intended working mode extending over a lengthier period of time and including, for example, periodical administration or infusion of fluids or medications in liquid form, the collection of blood samples and the like.
An unprotected released needle constitutes, however, a serious health hazard due to the fact that it may be contaminated with e.g. infectious agents originating from the patient's blood or other body fluids, in combination with the needle tip's inherent ability to easily penetrate skin. Hence, the medical personnel who are handling the released needle may acquire the corresponding disease, e.g. HIV or hepatitis, if by accident contacting it with their skin. In order to circumvent or alleviate the health hazards associated with such a released needle amongst other things, there has been much effort devoted to the development of various kinds of needle tip protectors with a special focus on automatic variants of a type which may be referred to as being “foolproof”.
Known automatic needle tip protectors of catheter instruments, utilized for introduction of a catheter tube, require means for immobilization of the needle tip protector relative the catheter hub during withdrawal of the needle from the catheter through the catheter hub. Upon disconnection of the needle tip protector from the catheter hub, in its state where it is protecting the needle tip, these means for immobilization are deactivated whereby the protector-needle tip assembly may be removed from the catheter hub-catheter assembly.
WO2011129753 describes a needle tip protector which is partially cut through with slits to allow compression of the protector when placed in the needle hub. The protector is thereby detachably held in the needle hub by a normal force in combination with inherent friction. The slits may extend essentially in the longitudinal direction of the protector, from the rear side to the front side.
Disadvantages of such means for immobilization include a relatively large variability of the force required to disconnect the protector from the catheter hub, which may adventure its intended function and safety. In this case, the large variability is due to the combination of a relative high connecting surface area between the protector and the catheter hub and the production related variability of the inner diameter of the catheter hub and the outer diameter of the protector.
U.S. Pat. No. 6,616,630 B1 discloses a safety IV catheter comprising a resilient spring clip as protector. When the needle is in the forward position, the presence of the needle forces parts of the spring clip into a position where these parts locks to the inside of the catheter hub, whereby movement of the spring clip relative the catheter hub is prevented. As the needle is withdrawn to a point where the tip passes these parts, the spring clip snaps into a position in which it is blocking access to the to the tip of the needle. Simultaneously, the part of the spring clip that previously locked to the inside of the catheter hub snap out of this position, whereby movement of the spring clip relative the catheter hub may occur.
For various reasons, including e.g. practical, economical and technical reasons, the above described spring clip, and similar marketed variants, are today by necessity made of metal and catheter hubs of a plastic material. Disadvantages of the combination of these materials in this application include the release of e.g. microscopic plastic chips and metallic particles by the scraping of the metal spring clip against the inside of the plastic catheter hub when the former is ejected from the latter upon withdrawal of the needle. These chips and particles may easily be flushed into the bloodstream of a patient upon normal use of the corresponding catheter, and thus represent a serious health hazard to the same.
GB2451153A by Poly Medicure Ltd discloses a protector capable of receiving a needle between opposing jaws attached to its base and capable of being influenced by the needle. The jaws may move between an expanded position in which they interact with an obstruction within the catheter hub. The jaws permit relative movement of the needle with the base when expanded, close around a needle tip as it passes the jaws, and release from the obstruction of the catheter hub when collapsed.
U.S. Pat. No. 5,135,504A describes a guard that may be made of a plastic material. The presence of the needle keeps the end of the guard flared out and thereby retained inside the catheter hub by e.g. a retaining ring held tightly therein until the needle is withdrawn from the catheter.
The function of the needle tip guards described in GB2451153A and U.S. Pat. No. 5,135,504A relies on the presence of one or several obstructions, e.g. protuberances or grooves, of the inside of the catheter hub for keeping the guards at place there until the needle is withdrawn from the hub. Disadvantages of the need of such obstructions include the need to use specially designed catheter hubs which are more expensive and difficult to produce in comparison to simpler standard catheter hubs.
Hence, a needle tip shielding device with improved means and structure for reversible spatial immobilization of the same relative the catheter hub, is desired.